<!DOCTYPE html>
<html lang="en">
    <head>
        <title>Responsive</title>
        <style>
            @media (min-width:600px) { /*如果宽度大于等于600px*/
                body{
                    background-color: red;
                }
            }
            @media (max-width:599px) { /*如果宽度小于等于599px*/
                body{
                    background-color: blue;
                }
            }
        </style>
    </head>
    <body>
        <h1>Welcome to my web page!</h1>
    </body>
</html>